Hypertension (high blood pressure) is the most important contributing cause because it damages the blood vessel lining exposing collagen where platelets aggregate to initiate a repair. If maintained hypertension can change the structure of blood vessels (narrow, deformed).[3]

A stroke usually presents with an abrupt onset of a neurologic deficit, attributable to a focal vascular lesion.[5] The neurologic symptoms manifest within seconds because neurons lack glycogen, so energy failure is rapid.[6]

Transient ischemic attack (TIA) also called a mini-stroke. This is a condition in which the blood flow is quickly restored and the brain tissue can fully recover and the symptoms are only transient, leaving no sequelae.[9] In order to diagnose this entity all neurologic signs and symptoms must have been resolved within 24 hrs without evidence of brain infarction on brain imaging.[10]

Subarachnoid haemorrhage where blood leaks out of blood vessels directly into or around the brain.[1] The neurologic symptoms are produced by the blood mass effect on neural structures, from the toxic effects of blood on the brain tissue, or by the increasing of intracranial pressure.[11]

Once a reduction in blood flow occurs, that lasts seconds the brain tissue suffers ischemia.[14][15] If the interruption of blood flow is not restored in minutes, the tissue suffers infarction followed by tissue death.[16] When the low cerebral blood flow persists for a longer duration, this may develop into an infarction in the border zones (areas of poor blood flow between the major cerebral artery distributions). In more severe instances, global hypoxia-ischemia causes widespread brain injury leading to a severe cognitive sequelae called hypoxic-ischemic encephalopathy.[17]

Strokes can also result from embolisms, furthermore, embolisms block small arteries, causing damage to occur.[4] Spontaneous rupture of a blood vessel in the brain causes a hemorrhagic stroke.[18] Another form of cerebrovascular disease includes aneurysms. Cerebral aneurysms can be genetic in nature, due to a wall deformity of the artery. Such aneurysms are common in individuals with genetic diseases ( connective tissue disorders, polycystic kidney disease, and arteriovenous malformations).[19]

The carotid arteries cover the majority of the cerebrum. The common carotid artery divides into the internal and the external carotid arteries. The internal carotid artery becomes the anterior cerebral artery and the middle central artery. The ACA transmits blood to the frontal parietal. From the basilar artery are two posterior cerebral arteries. Branches of the basilar and PCA supply the occipital lobe, brain stem, and the cerebellum.[20] Ischemia is the loss of blood flow to the focal region of the brain. This produces heterogeneous areas of ischemia at the affected vascular region, furthermore blood flow is limited to a residual flow. Regions with blood flow of less than 10 mL/100 g of tissue/min are core regions (cells here die within minutes of a stroke).The ischemic penumbra with a blood flow of <25 ml/100g tissue/min, remain usable for more time (hours).[21]

An ischemic cascade occurs where an energetic molecular problem arises. ATP consumption continues in spite of insufficient production, this causes total levels of adenosine triphosphate to decrease and lactate acidosis to become established (ionic homeostasis in neurons is lost). The downstream mechanisms of the ischemic cascade thus begins. Ion pumps no longer transport Ca2+ out of cell, this triggers release of glutamate, which in turn allows calcium into cell walls. In the end the apoptosis pathway is initiated and cell death occurs.[22]

Worldwide, it is estimated there are 31 million stroke survivors, though about 6 million deaths were due to cerebrovascular disease (2nd most common cause of death in the world and 6th most common cause of disability).[26]

Cerebrovascular disease primarily occurs with advanced age; the risk for developing it goes up significantly after 65 years of age. CVD tends to occur earlier than Alzheimer's Disease (which is rare before the age of 80). In some countries such as Japan, CVD is more common than AD.[medical citation needed]

In 2012 6.4 million US individuals (adults) had a stroke, which corresponds to 2.7% in the U.S. With approximately 129,000 deaths in 2013 (U.S.)[27]

Geographically, a "stroke belt" in the US has long been known, similar to the "diabetes belt"which includes all of Mississippi and parts of Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, North Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Texas, Virginia, and West Virginia.[28]